Exposure method and projection exposure apparatus

ABSTRACT

A projection exposure apparatus carries out scan exposure with illumination flux of slit(s) by moving a mask and a substrate in a direction of one-dimension at synchronized speeds with each other. The mask is inclined with a predetermined angle relative to the substrate in the direction of one-dimensional movement. The substrate is also moved in a direction of optical axis of projection optical system when moved in the direction of one-dimension, such that a central part of transfer area on the substrate is located on a best focal plane of projection optical system upon scan exposure.

This is a Division of application Ser. No. 08/377,254, filed Jan. 24,1995, which is a Reissue of U.S. Pat. No. 5,194,893, issued Mar. 16,1993.

This is one of five ( 5 ) reissue applications directed to variousdistinct and separate aspects of a projection exposure apparatus andmethod described in U.S. Pat. No. 5,194,893, which corresponds to U.S.application Ser. No. 07/845,065, filed Mar. 3, 1992. The first filedreissue application corresponds to application Ser. No. 08/377,254,filed Jan. 24, 1995. The other four reissue applications are divisionalapplications of application Ser. No. 08/377,254. The Ser. Nos. andfiling dates of the four divisional reissue applications are: Ser. Nos.09/481,507 filed Apr. 12, 2000; 09/515,503 filed Apr. 12, 2000;09/515,269 filed May 5, 2000; and 09/516,563 filed Jun. 15, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exposure method and a projectionexposure apparatus used in a lithography process in production ofsemiconductor elements, liquid crystal elements, or the like.

2. Related Background Art

There are two fundamental exposure methods conventionally used in suchprojection exposure apparatus. In one method, a photosensitive substratesuch as semiconductor wafer, glass plate, etc. is exposed to light in astep and repeat method through a projection optical system having anexposure field which can include the whole pattern of mask or reticle.The other is a scan method in which a reticle and a photosensitivesubstrate are opposed to each other at the both sides of a projectionoptical system under illumination light of arch slit illuminates thereticle, and the reticle and the photosensitive substrate are relativelyscanned for exposure under the illumination. Steppers employing theformer step and repeat exposure method are leading apparatus recentlyused in the lithography process. The step and repeat exposure method hasbeen improved in resolution, overlay accuracy, throughput, and so on,and became superior in these respects to aligners employing the latterexposure method. Therefore, it is considered that such steppersemploying the step and repeat exposure method will be leading inlithography for a while.

It is proposed for the step and repeat exposure method that thephotosensitive substrate and a best imaging plane of projection opticalsystem be relatively moved in a direction of optical axis duringexposure of one shot area in order to increase an apparent depth offocus of the projection optical system. This exposure method will behereinafter referred to as a successive focussing exposure method. Inthis successive focussing exposure method, the moving amount in theoptical axis direction is determined considering a real depth of focusof projection optical system and micro unevenness on the photosensitivesubstrate. The best imaging plane of projection optical system isarranged to be located between the top and the bottom of the unevennesson the photosensitive substrate surface during the movement.

Meanwhile, a novel scan exposure method achieving high resolution hasbeen recently proposed as a step and scan method on pp 424-433, SPIEvol. 1088, “Optical/Laser Microlithography II”, 1989. The step and scanmethod uses both a scan method, in which a reticle is one-dimensionallyscanned and a photosensitive substrate is also one-dimensionally scannedat a speed synchronized with the reticle speed, and a step method, inwhich the photosensitive substrate is stepped in a directionperpendicular to the scan exposure direction.

FIG. 11 is a drawing to illustrate a concept of the step and scanmethod. In FIG. 11, a shot area of one chip or multiple chips is scannedfor exposure with illumination light RIL of arch slit in the X-directionon a photosensitive substrate or wafer W. The wafer is stepped in theY-direction. In FIG. 11 a broken line shows a sequence of exposure ofstep and scan as will be hereinafter referred to as S and S, so that theS and S exposure is carried out on shot areas SA₁, SA₂, . . . , SA₆ inthis order, and then on shot areas SA₇, SA₈, . . . , SA₁₂ arranged inthe Y-direction in the center of the wafer. In the aligner of the S andS method as disclosed in the above-mentioned reference, an image ofreticle pattern illuminated by the arch slit illumination light RIL isfocussed on the wafer W through a one-quarter reduction projectionoptical system. Thus, a scan speed of reticle stage in the X-directionis controlled precisely to four times of that of wafer stage in theX-direction. The arch slit illumination light RIL is used because ademagnification system with a combination of refraction and reflectionelements is employed as the projection optical system, and advantage istaken of various abberations being zero in a narrow annular region apartat a certain distance from the optical axis. An example of suchreflection reduction projection system is disclosed in U.S. Pat. No.4,747,678.

However, it is impossible that the successive focussing exposure methodfor the step and repeat method is applied to the step and scan method.In detail, the step and repeat method takes such a structure that thereticle/wafer and the illumination optical flux/exposure flux cannot bemoved relative to each other in a direction perpendicular to the opticalaxis of the projection optical system, i.e., in a direction of waferplane, upon exposure of one shot area. Therefore, a point of pattern ina transfer region on a reticle may be exposed at a plurality of focuspoints by relatively moving the wafer and the projection optical systemin a direction of the optical axis upon exposure. In contrast, the stepand scan method takes such as structure that the reticle/wafer and theillumination flux/exposure flux may be moved relative to each other inthe direction perpendicular to the optical axis upon exposure of oneshot area. In this structure, if the wafer and the projection opticalsystem are moved relative to each other in the optical axis directionupon exposure, there would be mixed focussed parts and unfoccused partson the wafer depending on positions in the transfer region on thereticle. Accordingly, if the same successive focussing method as in thestep and repeat method is used for the S and S method, an increase in adepth of focus could not be expected, but degrading the resolution ofimage on the contrary.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anexposure method and a projection exposure apparatus, applying asuccessive focussing method to a scanning exposure method, to obtain anincrease in a depth of focus.

The object of the present invention, solving the above-described problemcan be achieved by a method for exposure in which a pattern IR formed ina transfer region on a mask R is subject to projection exposure througha projection optical system PL to be led onto an area to be exposure, orshot area, on a photosensitive substrate W, and the mask and thephotosensitive substrate are at least one-dimensionally, relativelyscanned with respect to a projection field IF of the projection opticalsystem PL: comprising, limiting a width of the area of pattern imageprojection on the photosensitive substrate W through the projectionoptical system PL to an approximately constant value in a direction ofone-dimensional scan; and inclining a local surface on thephotosensitive substrate W on which the pattern image is formed,relative to a best focal plane BF of the projection optical system PL inthe direction of one-dimensional scan.

Also, the object of the present invention can be achieved by aprojection exposure apparatus comprising: a projection optical system PLfor projecting a pattern IR formed in a transfer region on a mask R,onto an area to be exposed, or shot area, on a photosensitive substrateW; a mask stage 14 for one-dimensionally moving the mask R over a regionbeyond a width of the transfer region in a direction of movement; asubstrate stage 17, 18 for one-dimensionally moving the photosensitivesubstrate W in the direction of one-dimensional movement of the maskstage 14 at a speed synchronized with a movement speed of the mask stage14; an illumination system 1-13 for illuminating the mask R with anillumination flux for exposure, having a shape between a rectangle and aslit within the projection field IF of the projection optical system PLand having an approximately constant width in the direction ofone-dimensional movement; a substrate holder 16 for holding thephotosensitive substrate W on the substrate stage 17, 18 with apredetermined inclination angle with respect to the direction ofone-dimensional movement of illuminated area formed by the illuminationflux on the photosensitive substrate through the mask R and theprojection optical system PL; a holder drive system 21 for moving thesubstrate holder 16 in a direction of optical axis AX of the projectionoptical system such that a central part of the illuminated area on thephotosensitive substrate W is located near a best focal plane of theprojection optical system PL; and a control system 54 for controllingthe holder drive system 21 to maintain an imaging condition of patternimage of the mask R on the photosensitive substrate W withcorrespondence to a position in the illuminated area in the direction ofone-dimensional movement while scan exposure of pattern of the mask iseffected on the area to be exposed.

According to the present invention, in a projection exposure apparatusof scanning exposure method, the substrate holder is arranged to holdthe photosensitive substrate with the predetermined inclination to theone-dimensional scan direction of illumination area of illuminationflux, so that the best focal plane of projection optical system and theilluminated area on the photosensitive substrate may be inclinedrelative to each other. Further, the holder drive means is provided intranslate the substrate holder in the optical axis direction ofprojection optical system, such that the central part in the illuminatedarea on the photosensitive substrate is located at or near the bestfocal plane of the projection optical system. This arrangement allowscontinuous or discrete change of focussing of pattern image on thereticle for scan exposure. In other words, the depth of focus may beeffectively increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing to show a structure of a preferred embodiment of aprojection exposure apparatus according to the present invention;

FIG. 2 is a drawing to show an arrangement of blades constituting areticle blind;

FIG. 3A is a drawing to show a schematic structure near a wafer holder;

FIG. 3B is a drawing to show an illumination condition of illuminationflow from a leveling sensor on a wafer;

FIGS. 4A-4C are drawings to schematically show a method for exposureusing the projection exposure apparatus of the preferred embodimentaccording to the present invention;

FIG. 5 is a drawing to show a distribution of exposure in a direction ofthe optical axis at an arbitrary position on a wafer by the scanexposure;

FIGS. 6A and 6B are drawings to show a distribution of intensity ofimage provided at an arbitrary position on the wafer when the scanningexposure is effected by the projection exposure apparatus of thepreferred embodiment according to the present invention;

FIG. 7 is a drawing to show another example of blades constituting areticle blind;

FIG. 8 is a drawing to show a distribution of exposure in the opticalaxis direction at an arbitrary position on the wafer by the scanningexposure;

FIGS. 9A and 9B are drawings to show distributions of intensity of imagegiven at an arbitrary position on the wafer when the scanning exposureeffected by the projection exposure apparatus of another preferredembodiment according to present invention;

FIG. 10 is a drawing to show a distribution of exposure in the opticalaxis direction at an arbitrary position by the scanning exposure; and

FIG. 11 is a drawing to illustrate a concept of prior art step and scanexposure method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a drawing to show a structure of a preferred embodiment of aprojection exposure apparatus according to the present invention. Inthis embodiment, a projection optical system PL may be composed only ofrefraction elements or of a combination of refraction and reflectionelements to be a one-fifth reduction system, as being double sidetelecentric.

Illumination light for exposure from a mercury vapor lamp 1 is condensedat a secondary focus point by an ellipsoidal mirror 2. A rotary shutter3 is disposed at the secondary focus point to switch the illuminationlight between interception and transmission of light by a motor 4. Theillumination light passed through the shutter 3 is reflected by a mirror5, and enters an optical integrator or fly eye lens 7 through an inputlens 6. There are numerous secondary light source images formed at theoutput side of the fly eye lens 7, and the illumination light from thesecondary light source images is led through a beam splitter 8 into alens system or condenser lens 9.

Movable blades BL₁, BL₂, BL₃, BL₄ of a reticle blind mechanism 10 asshown in FIG. 2 are arranged on a back side focal plane of the lenssystem 9. The four blades BL₁, BL₂, BL₃, BL₄ are independently moved bya drive system 50. In this embodiment, edges of the blades BL₁, BL₂define a width of aperture AP in the X-direction or scan exposuredirection, and edges of blades BL₃, BL₄ a length of the aperture AP inthe Y-direction or stepping direction. The aperture AP defined by therespective edges of four blades BL₁-BL₄ is included in a circular imagefield IF of the projection optical system PL.

The illumination light takes a uniform distribution of illumination atthe position of the blind mechanism 10. The illumination light passedthrough the aperture AP of the blind mechanism 10 is guided through alens system 11, a mirror 12, and a main condenser lens 13 to a reticle Rto be illuminated. Then an image of the aperture AP defined by the fourblades BL₁-BL₄ of the blind mechanism 10 is focussed on a pattern planeon a lower surface of the reticle R.

The reticle R receiving the illumination light defined by the apertureAP is held by a reticle stage 14, which is movable at a uniform rate atleast in the X-direction on a column 15. The column 15 is incorporatedwith an unrepresented column holding a lens barrel of the projectionoptical system PL. The reticle stage 14 may be one-dimensionally movedin the X-direction and rotated by a small amount to correct its yawingby a drive system 51. A movable mirror 31 is fixed at an end of thereticle stage 14 to reflect a measurement beam from a laserinterferometer 30, so that the laser interferometer 30 may measure aposition of the reticle R in the X-direction and the amount of yawing ina real time manner. A fixed mirror or reference mirror 32 for the laserinterferometer 30 is fixed at the upper end of the lens barrel ofprojection optical system PL.

An image of pattern formed in a transfer region, for example arectangular region, of reticle R is imaged on a wafer W after reduced toone-fifth thereof by the projection optical system PL. The wafer W isheld together with a reference mark plate FM by a wafer holder 16 whichis rotatable by a small amount and inclinable at an arbitrary angle. Thewafer holder 16 is disposed on a Z-stage, which is movable by a smallamount in a direction of the optical axis AX or the Z-direction of theprojection optical system PL. The Z-stage 17 is mounted on an X,Y-stage18 which is two-dimensionally movable in the X- and the Y-directions inthe step and repeat method, and the X,Y-stage 18 is driven by a drivesystem 52. Further, a laser interferometer 33 measures a coordinateposition and a yawing amount of the X,Y-stage 18. A fixed mirror orreference mirror 34 for the laser interferometer 33 is fixed at thelower end of the lens barrel of the projection optical system, and amovable mirror 35 is fixed at one edge of the Z-stage 17. Since theprojection magnification is one fifth in this embodiment, a movingvelocity Vws of the X,Y-stage is set at one fifth of a velocity Vrs ofthe reticle stage in the X-direction 14 upon scan exposure.

Also in the present embodiment, there are provided an alignment system40, which employs a TTR (Through-The-Reticle) method to detect analignment mark or reference mark FM on the wafer W through the reticle Rand the projection optical system PL, and an alignment system 41, whichemploys a TTL (Through-The-Lens) method to detect an alignment mark orreference mark on the wafer W through the projection optical system at aposition below the reticle R. These alignment systems 40, 41 performrelative alignment of the reticle R and the wafer W before start of Sand S exposure or during the scan exposure. If the reference mark FM isa light emitting type, a photoelectric sensor 42 as shown in FIG. 1receives the light from the mark through the projection optical systemPL, the reticle R, the condenser lens 13, the lens system 11, 9 and thebeam splitter 8, whereby defining a position of the reticle R in thecoordinate system of the X,Y-stage 18 or defining a position ofdetection center of the respective alignment systems 40, 41. It shouldbe noted that these alignment systems are not always essential to thepresent invention.

As the length of the aperture AP of the blind mechanism 10 is madelonger in the Y-direction perpendicular to the scan direction orX-direction, the number of scannings in the X-direction or the number ofsteppings in the Y-direction on the wafer W may be reduced. However, thelength of the aperture AP in the Y-direction might better be changed bythe edges of the blades BL₃, BL₄ depending on size, shape, andarrangement of chip pattern on the reticle R. A preferred example isthat the facing edges of the blades BL₃, BL₄ coincide with street linesdividing the shot area on the wafer W. It is easy for this arrangementto adjust the length of aperture in correspondence with a size change inthe Y-direction of shot area. If a length in the Y-direction of one shotarea is over the maximum length of the aperture AP in the Y-direction,overlay exposure should be effected in the shot area to obtain seamlessexposure as disclosed in U.S. Pat. No. 4,924,257. Since the methoditself is not always essential to the present invention, detailedexplanation thereof is omitted.

Below explained with reference to FIG. 3A are the wafer holder 16inclinable at an arbitrary angle, and neighbors thereof. A motor 21 isprovided at the Z-stage 17, on the X,Y-stage 18 to drive the Z-stage 17in the direction of the optical axis AX. The wafer holder 16 is mountedon the Z-stage 17 with its center being supported. Leveling drivesections 20A, 20B are provided at periphery of the wafer holder 16, sothat the wafer W on the holder 16 may be inclined at an arbitrary angle.The leveling mechanism is disclosed for instance in U.S. Pat. No.4,770,531, so detailed explanation of the leveling mechanism is omitted.

A focus and leveling sensor is provided to control the inclination angleof the wafer W, which is constructed by a light projector 19A emittingan optical flux BPL of a wave length different from that of the exposurelight and a light receiver 19B receiving an optical flux BRL, which isthe optical flux BPL reflected by the wafer surface. A focus point, ofthe optical flux BPL from the focus and leveling sensor is coincidentwith a line including a point through which the optical axis of theprojection optical system PL passes on the wafer W. An example of thefocus and leveling sensor is disclosed in U.S. Pat. No. 4,558,949. Thusdetailed explanation is omitted.

The leveling drive sections 20A, 20B are driven by a command from aleveling control system 53 to determine an inclination amount of waferholder 16, based on leveling information from the light receiver 19B andinformation from the main control section 100. With constant feed backof leveling information from the light receiver 19B, a properinclination angle of the wafer W may be maintained. Further, focusinformation could be obtained to always locate an intersection with theoptical axis AX on the wafer W on the best imaging plane of theprojection optical system, with the information from the focus andleveling sensor. In this case, the motor 21 is driven by a command fromthe Z-stage control system 54 based on position information obtained bythe light receiver 19B, to drive the Z-stage 17 in the direction of theoptical axis AX.

The optical flux BPL is radiated on the wafer W as a slit light SLIinclined by 45° with respect to the rectangular illumination area AP′defined by the aperture AP of the blind as shown in FIG. 3B. By this,the position and the inclination of the wafer W in the Z-direction maybe controlled without influence from the directionality of circuitpattern in the chip area CP₁-CP₄ already formed on the wafer W. Althoughthere is shown only two points of the leveling drive section forexplanation, it is no doubt that drive on three points is better.

In the focus and leveling sensor as disclosed in the above-mentionedU.S. Pat. No. 4,558,949, parallel optical fluxes occupying a determinedara are impinged on the wafer surface, and reflection optical flux fromthe wafer surface is photoelectrically detected, for example using aquartered photodetector, to detect the inclination or the levelinginformation of the wafer surface. Then, a variable field stop may bedisposed inside the light projector 19A as disclosed for example in U.S.Pat. No. 4,902,900, to adjust the size and the shape of illuminationarea of parallel optical fluxes on the wafer surface, so that the sizeand the shape of the illumination area or detection area of the paralleloptical fluxes on the wafer surface is desirably made almost coincidentwith the rectangular illumination area AP′ defined by the aperture AP ofthe blind. By this, an average inclination of a local area in the shotregion on the wafer W corresponding to the rectangular illumination areaAP′ may be effectively detected, the inclination amount of the wafersurface or wafer holder 16 may be controlled with a higher precision.

An operation of the preferred embodiment of the projection exposureapparatus will be below explained. The main control section 100 totallydominates the sequence and control of the operation as shown in FIG. 1.A fundamental operation of the main control section 100 is that, basedon inputs of position information and yawing information from the laserinterferometer 30, 33 and on inputs of speed information from atachogenerator or the like in the drive systems 51, 52, reticle patternand the wafer pattern in one shot area are relatively moved within adetermined alignment error of the relative position while keeping adetermined ratio of speed of the reticle stage 14 and the X,Y-stage 18upon scan exposure. In addition to the fundamental operation, the maincontrol section 100 of the present embodiment is characterized in thatthe best imaging plane or the best focal plane of the projection opticalsystem PL (projection image plane of transfer region of the reticle) isinclined relative to the shot area on the wafer W, the central part oftransfer region (corresponding to illumination area AP′) on the shotarea is always located at or near the best imaging plane or best focusposition of the projection optical system PL, and thereby the focuscondition of pattern image of reticle is continuously or discretelychanged with correspondence to a position in the illumination area inthe one-dimensional scan direction during the scan exposure, bycontrolling the leveling control system 53 and the Z-stage controlsystem 54 together.

FIGS. 4A-4C schematically show a method for exposure using theprojection exposure apparatus of the preferred embodiment according tothe present invention. Positions 1-9 in a circuit pattern IR on thereticle R correspond to positions 1-9 on the wafer W, respectively. Thewafer W is inclined relative to the pattern IR. The circuit pattern IRis displayed just above the wafer W, and a projection ratio of thecircuit pattern IR is 1 on the wafer W for convenience of explanation.In the drawings, there are three optical fluxes LR, LC, LL shown out ofthe exposure flux defined by the single aperture AP. The optical fluxesLR, LL of the three are defined by the blades BL₁, BL₂ as shown in FIG.2, and symmetrically arranged before and after the optical axis AX inthe scan exposure direction. The width between the optical fluxes LR andLL corresponds to a width of the aperture AX in the X-direction,representing illumination range of exposure flux in the scanningdirection. The intensity of exposure flux is uniform in thisillumination range. The optical flux LC has a main light beam passingthrough the center of the illumination range of exposure flux. The mainlight beam corresponds to the optical axis AX of the projection opticalsystem PL. The best imaging plane of the projection optical system PL isshown by a broken line BF.

The scan exposure is controlled such that the X,Y-stage 18 is driven inthe X-direction and the Z-stage 17 is simultaneously driven in thedirection of the optical axis AX, to always locate the approximatecenter in the illumination area of the wafer W (corresponding to theapproximate center of illumination range of exposure flux) on the bestimaging plane BF of the projection optical system PL. If the width ofillumination area AP′ on the wafer W is defined as D_(ap), theinclination angle between the illumination area AP′ on the wafer W andthe best imaging plane BF as θ₁, and a width in the optical axis of thedepth of focus of the projection optical system PL (DOF) as ΔZ_(f), atleast one of the depth D_(ap) of the illumination area and inclinationangle θ₁ is adjusted to satisfy the following relation: D_(ap)·sinθ₁≧ΔZ_(f). A theoretical depth of focus is normally given by an equationΔZ_(f)=λ/NA², where λ is an exposure wave length, and NA is a numericalaperture of projection optical system.

A positional relation of wafer W and pattern IR to the exposure fluxjust after the scan exposure start is shown in FIG. 4A. Noting theposition 2 in the circuit pattern IR, it is just entered within theillumination range of exposure flux. However, an image at the position 2on the wafer W is in a condition of defocusing and the distribution ofintensity of projection image has a gentle peak. FIG. 4B shows acondition after further scan exposure, in which the position 2 on thewafer W is located on the best imaging plane BF. In this condition, theimage at the position 2 is in the best focus condition, presenting asteep peak in the intensity distribution of image. When the wafer ismoved as shown in FIG. 4C, the position 2 is in the condition ofdefocussing opposite to the condition as shown in FIG. 4A, again showinga gentle peak in the intensity distribution of image.

FIG. 5 shows a distribution of exposure amount in the direction of theoptical axis AX or in the Z-direction at the position 2 on the wafer Wby the above-described scan exposure or uniform rate scan. The exposureamount at the position 2 is uniform in the Z-directional range ofD_(ap)·sin θ₁ (the depth of focus DOF). FIGS. 6A and 6B show resultantdistributions of intensity of image at the position 2. The intensitydistributions ER, EC, EL in FIG. 6A represent intensities of imagesobtained from the optical fluxes LR, LC, LL, respectively. Adistribution of intensity E as shown in FIG. 6B represents anintegration of image intensity obtained from exposure flux of fluxes LR,LC, LL. Since the position 2 receives the optical fluxes (opticalenergy) while in the illumination range of exposure flux, the integratedintensity distribution E shows a gentle peak. As seen in FIG. 6B, awidth in which the intensity is over an exposure amount E_(th) enough toeffect photosensitizing of photo resist on the wafer W, i.e., tocompletely remove the photo resist, becomes relatively broad,accordingly.

In order to narrow the width W, there may be provided at least two peaksin the one-dimensional scan direction of scan exposure in thedistribution of intensity of rectangular illumination flux. For example,as shown in FIG. 7, the reticle blind mechanism may be arranged to havesuch a structure that a central portion of the aperture AP isintercepted (double slit aperture). It may be achieved by providing theblade BL₄ of the four blades of the blind mechanism 10 with aY-directionally extending interception branch to intercept light in adetermined width in the X-direction at the center of the aperture AP. Incase of use of such blind mechanism, the exposure amount in thedirection of the optical axis AX or in the Z-direction is distributed asshown in FIG. 8 at the position 2 on the wafer W by the scan exposure oruniform rate scan. The exposure at the position 2 shows two identicalintensity ranges located near the both ends of the Z-directional rangeof D_(ap)·sin θ₁ (depth of focus DOF). By this arrangement, only theoptical fluxes LR, LL in the exposure fluxes as shown in FIG. 4 possiblyhave intensities in the distribution.

FIGS. 9A and 9B show distribution of intensity of image obtained at anarbitrary position, for example at the position 2 as above described, onthe wafer W when the scan exposure of uniform rate scan is conducted byusing such optical fluxes. The intensity distributions ER′, EL′ as shownin FIG. 9A are distributions of intensity of images given by the opticalfluxes LR, LL, respectively. An intensity distribution E′ as shown inFIG. 9B is an integration of the intensity distributions ER′, EL′. Theintensity distribution E′ shows a steeper peak than that as shown inFIG. 6B. A width W′ in which the intensity is over the exposure amountE_(th) enough to effect photosensitizing of photo resist on the wafer Wto completely remove it, is narrower than the width W as shown in FIG.6B.

Furthermore, three peaks may be employed in the one-dimensional scandirection of scan exposure in a distribution of intensity of rectangularillumination flux. For this purpose, a reticle blind mechanism isprovided with blades with three slits in the aperture. FIG. 10 shows adistribution of exposure in the direction of optical axis AX at theposition 2 on the wafer W by the similar scan exposure. At the position2, three regions in the Z-direction have almost identical intensities ofexposure, one near the best imaging plane BP, and two near the both endsof the Z-directional range of D_(ap)·sin θ₁ (depth of focus DOF).Therefore, exposure flux reaching the wafer W includes fluxescorresponding to the optical fluxes LR, LC, LL, as shown in FIGS. 4A-4C.The optical fluxes LR, LL are symmetrical with respect to the opticalflux LC having the same optical axis AX of the projection opticalsystem. In case of scan exposure with the flux with three peaks in thedistribution of intensity in the illumination range, a distribution ofintensity of image projected onto the wafer W shows a steeper peak thanthe distribution of intensity E as shown in FIG. 6B. A width ofprojected image will be narrower than the width W as shown in FIG. 6B,accordingly.

Comparing two slits and three slits in the one-dimensional direction ofscan exposure in the intensity distribution of rectangular illuminationflux if the optical intensity of illumination flux is almost identical,exposure with three slits allows faster moving speed of the X,Y-stageand gives a higher throughput. This is opposite to the successivefocussing exposure method conventionally known in U.S. Pat. No.4,869,999.

In the above examples, the blades of the blind mechanism have a lightintercepting portion. In another arrangement, the same effect may beobtained by an interception member such as ND filter having dimensionsand shape corresponding to a region to be intercepted at a positionconjugate to the circuit pattern IR in the optical path. Furthermore,although the wafer surface is inclined before the scan exposure in theabove examples, the inclination of the wafer holder 16 may be controlledtogether with the Z-directional position of the wafer surface by usingdetection information of the focus and leveling sensor at the time ofscan exposure start.

What is claimed is:
 1. A method for exposure in which a pattern formedin a transfer region on a mask is subject to projection exposure througha projection optical system to be led onto an area to be exposed on aphotosensitive substrate, and said mask and photosensitive substrate areat least one-dimensionally, relatively scanned with respect to aprojection field of said projection optical system: comprising, limitinga width of said area of pattern image projected on said photosensitivesubstrate through the projection optical system to an approximatelyconstant value in a direction of one-dimensional scan; and inclining alocal surface on said photosensitive substrate on which said patternimage is formed, relative to a best focal plane of said projectionoptical system in the direction of one-dimensional scan.
 2. A method forexposure according to claim 1, wherein a central part of said localsurface in the direction of one-dimensional scan on said photosensitivesubstrate, on which said pattern image is formed, substantiallycoincides with said best focal plane of projection optical system whenscanned for exposure.
 3. A method for exposure according to claim 1,wherein, defining a width of local surface on the photosensitivesubstrate in the direction of one-dimensional scan, on which saidpattern image is formed as D_(ap), an angle of inclination between saidlocal surface and said best focal plane as θ₁, and a depth of focus ofsaid projection optical system in a direction of optical axis as ΔZ_(f),the following relation is satisfied by adjusting at least one of saidwidth D_(ap) of the pattern image area and said inclination angle θ₁;D_(ap)·sin θ₁≧Z_(f).
 4. A method for exposure according to claim 1,wherein, the order to limit said width of pattern image area in thedirection of one-dimensional scan, a shape of illumination flux forexposure is made rectangular on said mask to be illuminated thereby, andan intensity distribution of said rectangular illumination flux has atleast two peaks in the direction of one-dimensional scan.
 5. Aprojection exposure apparatus comprising: a projection optical systemfor projecting a pattern formed in a transfer region on a mask, onto anarea to be exposed on a photosensitive substrate; a mask stage forone-dimensionally moving said mask over a region beyond a width of saidtransfer region in a direction of movement; a substrate stage forone-dimensionally moving said photosensitive substrate in the directionof one-dimensional movement of said mask stage at a speed synchronizedwith a movement speed of said mask stage; illumination means forilluminating said mask with an illumination flux for exposure, having ashape between a rectangle and a slit within the projection field of saidprojection optical system and having an approximately constant width inthe direction of one-dimensional movement; a substrate holder theholding said photosensitive substrate on said substrate stage with apredetermined inclination angle with respect to the direction ofone-dimensional movement of illuminated area formed by said illuminationflux on said photosensitive substrate through said mask and saidprojection optical system; holder drive means for moving said substrateholder in a direction of optical axis of said projection optical systemsuch that a central part of said illuminated area on said photosensitivesubstrate is located near a best focal plane of said projection opticalsystem; and control means for controlling said holder drive means tomaintain an imaging condition of pattern image of said mask on saidphotosensitive substrate with correspondence to a position in saidilluminated area in the direction of one-dimensional movement while scanexposure of pattern of said mask is effected on said area to be exposed.6. A scanning exposure apparatus in which a substrate is exposed with anenergy beam by moving a mask and the substrate relative to the energybeam, comprising: a projection system, arranged in a path of the energybeam, which is a reduction system to project a reduction image of apattern formed on the mask onto the substrate, an image field of theprojection system being a circular image field; an illumination system,disposed along the path of the energy beam, which distributes the energybeam within a specified slit-shaped region in the image field of theprojection system; a first stage, disposed on an object surface side ofthe projection system, which is movable in a first direction whileholding the mask during scanning exposure of the substrate; a firstinterferometer which measures positional information of the first stagein the first direction during the scanning exposure; a second stage,disposed on an image surface side of the projection system, which ismovable in a second direction while holding the substrate during thescanning exposure, wherein the specified region is a substantiallyrectangular region which diametrically extends within the circular imagefield in a direction substantially perpendicular to the second directionand wherein a width of the specified region in the second direction isshorter than a length of the specified region in a directionperpendicular to the second direction; a second interferometer, whichmeasures positional information of the second stage in the seconddirection during the scanning exposure; a driving unit connected to thefirst and second interferometers to adjust a relative relationshipbetween the mask and the substrate based on the positional informationmeasured by the first and second interferometers during the exposure,said driving unit including a first driving system to move the firststage and a second driving system to move the second stage, wherein thefirst stage is moved at a first speed and the second stage is moved at asecond speed which is different from the first speed and a ratio betweenthe first speed and the second speed is determined in accordance with areduction magnification of the projection system; a detection unitdisposed apart from the second stage to detect inclination informationof the substrate during the scanning exposure, said detection unitincluding a projecting element to project a detection light onto thesubstrate within the specified region and a receiving element to receivethe detection light reflected on the substrate; and an adjustmentsystem, connected to the detection unit, which controls inclination ofthe substrate during the scanning exposure to adjust a relativeinclination between the substrate and an image surface of the projectionsystem in the specified region based on the information detected by thedetection unit.
 7. An apparatus according to claim 6, wherein: theadjustment system controls the inclination of the substrate by movingthe substrate at three points.
 8. An apparatus according to claim 6,wherein: the adjustment system controls the inclination of the substrateso that the substrate substantially coincides with an image surface ofthe projection system at a center of the specified region.
 9. Anapparatus according to claim 6, wherein: the first interferometermeasures rotational information of the first stage during the scanningexposure.
 10. An apparatus according to claim 9, wherein: the rotationalinformation includes yawing information.
 11. An apparatus according toclaim 9, further comprising: a reflection member, disposed in the pathof the energy beam, which reflects the energy beam, wherein the seconddirection is substantially parallel to a plane which includes an axis ofthe energy beam incident on the reflection member and an axis of theenergy beam reflected by the reflection member.
 12. An apparatusaccording to claim 6, wherein: the second interferometer measuresrotational information of the second stage during the scanning exposure.13. An apparatus according to claim 6, further comprising: a firstreference reflection surface for the measurement of the firstinterferometer, arranged on a barrel of the projection system; and asecond reference reflection surface for the measurement of the secondinterferometer, arranged on the barrel of the projection system.
 14. Anapparatus according to claim 6, further comprising: a reference member,disposed on the second stage, which defines a relationship between thepositional information measured by the first interferometer and thepositional information measured by the second interferometer.
 15. Anapparatus according to claim 6, wherein: speed information of the firstand second stages is detected during the scanning exposure.
 16. Anapparatus according to claim 6, further comprising: a reflection member,disposed in the path of the energy beam, which reflects the energy beam,wherein the second direction is substantially parallel to a plane whichincludes an axis of the energy beam incident on the reflection memberand an axis of the energy beam reflected by the reflection member. 17.An apparatus according to claim 6, wherein: the projection system iscomposed only of refraction elements, and wherein an optical axis of theprojection system is substantially in one straight line.
 18. Anapparatus according to claim 17, wherein: the projection system istelecentric on the image surface side and on the object surface side.19. A scanning exposure method in which a substrate is exposed with anenergy beam, comprising: moving a mask in a first direction relative tothe energy beam during scanning exposure; moving a substrate in a seconddirection relative to the energy beam during the scanning exposure,wherein the mask is moved at a first speed and the substrate is moved ata second speed which is different from the first speed, and a ratiobetween the first speed and the second speed is determined in accordancewith a reduction magnification of a projection system; distributing theenergy beam within a specified rectangular region in a circular imagefield of the projection system during the scanning exposure, wherein awidth of the specified region in the second direction is shorter than alength of the specified region in a direction perpendicular to thesecond direction; measuring positional information of the mask by usinga first interferometer system during the scanning exposure; measuringpositional information of the substrate by using a second interferometersystem during the scanning exposure; adjusting a relative relationshipbetween the mask and the substrate based on the positional informationmeasured by the first and second interferometer systems during thescanning exposure; detecting, during the scanning exposure, inclinationinformation of the substrate by projecting detecting light within thespecified region onto the substrate; and controlling inclination of thesubstrate during the scanning exposure to adjust a relative inclinationbetween the substrate and an image surface of the projection system inthe specified region based on the detected inclination information. 20.A method according to claim 19, further comprising: measuring rotationalinformation of the mask by using the first interferometer system; andmeasuring rotational information of the substrate by using the secondinterferometer system.
 21. A method according to claim 20, wherein theinclination of the substrate is controlled so that the substratesubstantially coincides the image surface of the projection system at acenter of the specified region.
 22. A method according to claim 21,further comprising: detecting speed information of the mask and thesubstrate during the scanning exposure.